Sprinkler Blowout vs. Draining: Which Winterizing Method Is Right for Long Island Systems?

30 Sep Sprinkler Blowout vs. Draining: Which Winterizing Method Is Right for Long Island Systems?

For almost every lawn sprinkler system on Long Island, a compressed-air blowout is the right winterizing method. Manual drain and automatic drain valves only work on systems that were built with drains at every low point and enough slope to carry water to them, and very few residential systems in Suffolk County or Nassau County were installed that way. Blowout pushes water out of the pipe regardless of grade, which is why it has been the standard here for decades and why McCormack Irrigation’s winterizing service is built around it.

This post explains how each of the three methods works, why Long Island’s soil and pipe depth favor blowout, the pressure limits manufacturers publish, and where a do-it-yourself blowout tends to go wrong.

The Three Ways to Winterize an Irrigation System

1. Manual drain

A manual drain system has shutoff valves installed at the lowest points of the mainline and at the end of each lateral. To winterize, you close the supply, open every drain valve, and let gravity carry the water out. It only works if the installer sloped every pipe run toward a drain and placed drains at every low spot. Hunter Industries notes that attempting the manual drain method on a system not designed and installed for it “may lead to negative results,” which in plain terms means water left in the low spots and a cracked fitting in March. Their guidance is on Hunter’s winterizing your irrigation system page.

2. Automatic drain valves

Automatic drain valves are spring-loaded fittings at low points that open whenever line pressure drops below a set threshold. When the supply is closed and the zones are bled, the valves open and drain the laterals on their own. They share the same weakness as manual drains: they only empty what gravity brings to them. They also add a small opening at every low point, which on Long Island’s sandy soil is an invitation for grit to enter the line each time the valve cycles.

3. Compressed-air blowout

A blowout connects a compressor to the mainline downstream of the backflow device and pushes air through each zone in turn, forcing water out through the heads. It does not depend on slope, drain placement, or how the system was originally installed. Both Hunter and Rain Bird describe blowout as the recommended method when the system type is unknown, which covers most homeowners who inherited a system with the house.

Why Blowout Is the Standard on Long Island

Three local conditions push Long Island toward blowout over draining.

• Shallow pipe burial. Residential laterals across Suffolk County are typically buried just below sod depth in polyethylene pipe, well above the frost line. Every foot of that pipe has to be empty, not just the low points.
• Flat outwash plain and rolling moraine. The South Shore and central Suffolk are nearly flat, so lines have no natural slope to drain along. The North Shore moraine is the opposite problem, with lines running up and down grade and water pooling in every dip.
• Sandy soil and fast drainage. Long Island’s sandy soils settle and shift after installation, which means a line that was sloped toward a drain in year one may hold a belly by year five. Air does not care about a belly. Gravity does.

McCormack has winterized systems from Huntington to the Hamptons since 2001, and the pattern is consistent: systems that were only drained show up in April with split fittings, cracked manifolds, and heads that will not seat. Blown-out systems come back with a routine spring turn on.

Pressure and Airflow: What the Manufacturers Publish

A blowout is only safe inside the pressure and time limits the pipe and heads are rated for. These figures come from the manufacturers, not from us.

• Polyethylene pipe: Hunter lists a maximum of 50 PSI. Most Long Island residential systems are poly.
• PVC pipe: Hunter lists a maximum of 80 PSI.
• Airflow: Hunter’s sizing rule is to divide the largest zone’s total gallons per minute by 7.5 to find the cubic feet per minute (CFM) the compressor needs to deliver. Rain Bird’s homeowner guidance calls for a compressor rated at 185 CFM or greater to keep continuous flow through a full zone.
• Time per zone: Rain Bird advises no more than two minutes of air on any circuit at a time, using two or more short cycles until only a fine mist appears, because dry pipe under continuous air builds friction heat that can melt gear-drive rotor seals and damage fittings. That guidance is in Rain Bird’s blowout season tips.

The pressure and volume numbers matter in different ways. Too much PSI cracks fittings and pops heads off risers. Too little CFM means the air moves over the water instead of pushing it out, and the zone looks clear while water sits in the bottom of the pipe. A small pancake compressor from a hardware store can reach 50 PSI but cannot supply the volume, and that is the most common reason a DIY blowout fails.

How the Backflow Device Is Handled

The backflow preventer is the one component that should never see compressed air. Hunter’s winterization technical bulletin states that compressed air should not be blown through any backflow device. The correct sequence is:

1. Close the isolation ball valves on both sides of the backflow assembly.
2. Connect the compressor to a fitting downstream of the backflow, never upstream.
3. Blow out every zone, farthest zone first, working back toward the compressor.
4. Disconnect the compressor and release all air pressure.
5. Open and close the backflow isolation valves several times to release trapped water.
6. Leave the isolation valves partially open at about a 45 degree angle and open the test cocks so any remaining water has room to expand.

Because the backflow is opened and manipulated during winterization, it needs its annual certification again in spring. McCormack’s backflow testing is performed by New York State certified testers, with the paperwork filed with your local water district.

DIY Blowout: The Risks, Stated Plainly

A homeowner with the right compressor and a clear understanding of the system can blow out their own lines. Most of the problems we repair in spring come from one of these mistakes:

• Using a compressor that hits the PSI target but lacks the CFM to move water, leaving lines partly full.
• Running air with the backflow isolation valves open, damaging the checks inside the assembly.
• Blowing a zone for five or ten minutes straight and melting rotor seals with friction heat.
• Standing over heads or valves during the blowout. Both manufacturers say not to, and both call for eye protection.
• Forgetting the zone that runs off a separate valve, the drip zone, or the hose bib tied into the mainline.

None of these is dramatic on the day it happens. They show up in April as a wet spot in the lawn, a manifold that leaks under pressure, or a backflow that fails its test. If you have already had a rough DIY blowout, our sprinkler repair service can inspect the system and fix what froze.

What McCormack’s Winterizing Service Includes

Our crews arrive with truck-mounted compressors sized for residential and commercial zones, regulate pressure for the pipe type in your yard, isolate and drain the backflow properly, and blow out heads, piping, fittings, solenoid valves, manifolds, exposed plumbing, and hose bibs. The controller is set to off so nothing runs until spring. Every technician is trained, uniformed, in-house staff. We do not use subcontractors, and that consistency is reflected in a 4.9 out of 5 rating across 328 Google reviews and an A+ rating with the Better Business Bureau.

Book Your Sprinkler Blowout

McCormack Irrigation has provided sprinkler winterization across Suffolk County and Nassau County since 2001. Family owned and operated, with in-house crews on every job. Call (631) 744-1500 or schedule your blowout online before the first hard freeze reaches your neighborhood.